In materials science, a substrate is understood to refer to a material to be treated. The surface of the substrate is often processed or coated. In the present patent application, the substrate includes the body having a coating whose barrier effect is to be determined. The substrate can therefore include in particular a base body made of a homogeneous material to which a coating has already been applied but is itself not intended to be the object of testing of the barrier effect thereof.
The term coating is understood in production technology to refer to a main group of the production processes according to DIN 8580 that are used to apply a firmly adhering layer of amorphous material to the surface of a workpiece. The term coating denotes both the corresponding process and the applied layer itself. A coating may be made of a thin or thick layer or a plurality of interconnected layers. Coating methods are classified according to the type of layer application into chemical, mechanical, thermal, and thermomechanical methods.
A barrier is understood in the present patent application to refer to an obstacle. Accordingly, a barrier effect of a coating is a measure of the effect of the coating as an obstacle to a medium. Such a medium may be a fluid, that is, a gas or a liquid.
The invention concerns a method via which the barrier qualities of layers, in particular vapor-deposited layers (for example layers applied via physical gas-phase deposition or physical vapor deposition, PVD), layers deposited via chemical reactions (for example by plasma enhanced chemical vapor deposition, PECVD or plasma induced chemical vapor deposition, PICVD), layers applied by cathode deposition or sputtering, or galvanically deposited layers or lacquer layers that can be measured and quantitatively evaluated on a suitable substrate.
A method for measuring the gas permeability of a coating on a plastic wall is known from U.S. Pat. No. 6,658,919. U.S. Pat. No. 8,266,944 B2 describes a method for evaluating the scratch resistance of a plastic resin.
Especially in the area of plastic coatings, particularly in the area of coating of plastic spectacle lenses with nonreflective coatings, it is known that under the effect of moisture, plastics can absorb this moisture from the environment and thus increase their volume. In cases where a non-moisture-permeable coating is present on the plastic, this leads to local areas of swelling referred to as distortions that warp the surface of the coated (tempered) plastic to such an extent that this can be observed as optical interference.
A method is known from company-internal prior art and DE 10 2013 104 846 B3 for the measurement of the barrier qualities of such plastic/coating systems with respect to moisture in which the water content of the plastic substrate is measured via infrared absorption in order to then calculate the transmission factor of water through the layer system located on the plastic. However, this infrared measurement technique is only an indirect method with respect to the distortions occurring on penetration of water, and it cannot provide any data on the swelling behavior of the plastic.